Cyclic AMP-dependent protein kinase activity and protein phosphorylation in zones of the adrenal cortex

Steroidogenesis is not stimulated by ACTH in the inner zone of the guinea pig adrenal cortex; adenylate cyclase is normally stimulated. To further explore the lack of a steroidogenic response to ACTH in the inner zone, cAMP-dependent protein kinase activity and protein phosphorylation were examined in the outer and inner adrenocortical zones. To summarize: total cAMP-dependent protein kinase activity was 40% higher in the outer zone than in the inner zone; of the total cAMP-dependent protein kinase activity, cytosol contained 80% for the outer and 70% for the inner zone. In both zones only the type II isozyme was present. Qualitative and quantitative differences in protein phosphorylation were noted for the two zones.